As indicated in the American review "Jeweller's Circular-Keystone, February 1977", page 119, FIG. 4, electronic watches equipped with an alarm system generally use a bipolar transistor as a power output stage, controlling the alarm device. The bipolar transistor is excited by a signal coming from the integrated circuit of the watch, but is not comprised therein as it is not made in C-MOS technology.
It would be useful to integrate this component on the watch chip which would save time during the assembly thereof and would contribute in reducing the number of interconnections between the integrated circuit and components exterior thereto, such as the motor and the alarm transducer. However, and as indicated in the specifications of the integrated circuit E 010, made in C-MOS technology, for a watch having a stepping Microelectronic-Marin motor, the four motor control transistors themselves occupy an area of 0.914.times.2.032 mm, which is slightly greater than half of 1.803.times.2.032 mm of the watch chip.
The example of the E 010 integrated circuit, discussed above, shows that the power transistors occupy a large surface when they are made in C-MOS technology. On the other hand, to make the equivalent of a bipolar power transistor with Vce Sat=100 mV, it is necessary for the resistance of the drain-source channel of the MOS transistor to be of the order of 70 ohms. Such transistors have already been made for the control of stepping motors.